An achromatic 3D STED measuring optical process and optical method, based on a conical diffraction effect or an effect of propagation of light in uniaxial crystals, including a cascade of at least two uniaxial or conical diffraction crystals creating, from a laser source, all of the light propagating along substantially the same optical path, from the output of an optical bank to the objective of a microscope. A spatial position of at least one luminous nano-emitter, structured object or a continuous distribution in a sample is determined.
Reconstruction of the sample and its spatial and/or temporal and/or spectral properties is treated as an inverse Bayesian problem leading to the definition of an a posteriori distribution, and a posteriori relationship combining, by virtue of the Bayes law, the probabilistic formulation of a noise model, and possible priors on a distribution of light created in the sample by projection.